bug#8789: 23.3; debug backtrace buffer changes window on step-through

[martin rudalics <rudalics@gmx.at>]

 >> Thanks for your fixes.  I'll check the next Windows binary. - Drew
 >
 > I have not yet been able to do that (no Windows binary),

It's trivial to get the change from say

http://lists.gnu.org/archive/html/emacs-diffs/2012-09/msg00266.html

and apply it.  You don't have to rebuild Emacs for this change, just recompile
debug.el.

 > but here is some more
 > info.  (I have not customized `debugger-bury-or-kill' - the value is still
 > `bury'.)
 >
 > Sometimes I can grab the border of the *Backtrace* frame, as usual, and resize
 > it (even though it goes back to the default size when I hit `d', as described
 > earlier).

This should have changed now.

 > But sometimes I cannot: as soon as I touch the mouse to the frame edge and try
 > to drag it, the frame disappears!  I can just touch it (e.g. click it) without
 > it disappearing, but as soon as I try to drag the touched edge, the frame
 > disappears.  It does not matter which edge (e.g. bottom or right) I try to drag.
 >
 > No idea what is going on here - I have never seen anything like this.
 >
 > This happpens systematically when I enter the debugger in a certain context, and
 > it never seems to happen otherwise.  But that context is far too complex to try
 > to communicate.  Suffice it to say that this happens.
 >
 > When it happens I see nothing additional in *Messages*, and there is no crash.
 > The *Backtrace* frame just disappears, and the mode line indicates that I am no
 > longer in a recursive edit - IOW, the debugger is exited.  And if I explicitly
 > visit buffer *Backtrace*, I see that it is indeed empty.
 >
 > It is as if trying to drag the frame edge is (sometimes) the equivalent of
 > hitting `q' in the debugger.

Looks like.  Try with my change.  Later we can try to put in some code
immediately before the call to `quit-restore-window' to investigate the
last command or input event that triggers this.

martin